1. Field of the Invention
This invention relates to a semiconductor integrated circuit device. More particularly, this invention relates to a semiconductor integrated circuit device which has a semiconductor memory device and a logic circuit formed on a single semiconductor substrate.
2. Description of the Related Art
In the field of a semiconductor integrated circuit (LSI) which has a semiconductor memory and a logic circuit formed on a single substrate, the need for a rewritable flash memory as a semiconductor memory has recently being increasing.
In a combined flash memory/logic LSI, a low-voltage power supply is used in the logic circuit to meet low-power requirements and the like. In the flash memory, a high-voltage power supply necessary to write and erase the data is used. Since the power supply of the flash memory differs from that of the logic circuit, it is necessary to detect the voltage levels of a plurality of power supplies at the time when the power supply of the LSI is turned on. A circuit for such a purpose has been proposed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-100974.
However, even if a conventional detecting circuit has sensed that the power supply has reached a sufficient voltage level for the operation of the logic circuit, the voltage level might not be sufficient for the operation of the analog circuit. In such a case, the logic circuit operates properly, but the analog circuit operates erroneously.